Stators For Downhole Motors, Methods For Fabricating The Same, And Downhole Motors Incorporating The Same

ABSTRACT

The present invention recites a method of fabricating a stator for a downhole motor, the method comprising the steps of providing a stator tube having an interior surface and applying a bonding agent to the interior surface of the stator tube. Additionally, a mandrel is positioned within the stator tube, the mandrel having an outer geometry that is complimentary to a desired inner geometry for the stator. Furthermore, a reinforcing material is introduced into the stator tube to fill space between the mandrel and the interior surface of the stator tube and subsequently solidified to bond the reinforcing material to the interior surface of the stator tube. The mandrel is then removed from the bonded stator tube and reinforcing material such that a stator is fabricated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 12/617,864, filed Nov. 13, 2009, which is herein incorporatedby reference.

BACKGROUND OF THE INVENTION

Downhole motors (colloquially known as “mud motors”) are powerfulgenerators used in drilling operations to turn a drill bit, generateelectricity, and the like. As suggested by the term “mud motor,” mudmotors are often powered by drilling fluid (e.g., “mud”). Such drillingfluid is also used to lubricate the drill string and to carry awaycuttings and, accordingly, often contains particulate matter such asborehole cuttings that can reduce the useful life of downhole motors.Accordingly, there is a need for new approaches for cost effectivelymanufacturing downhole motors and downhole motor components that arecost effective and facilitate quick replacement in the field.

SUMMARY OF THE INVENTION

The present invention generally relates to a method of fabricating astator for a downhole motor wherein the method comprises the steps ofproviding a stator tube having an interior surface, applying a bondingagent to the interior surface of the stator tube, positioning a mandrelwithin the stator tube, the mandrel having an outer geometry that iscomplimentary to a desired inner geometry for the stator and introducinga reinforcing material into the stator tube to fill space between themandrel and the interior surface of the stator tube. Additionally, thereinforcing material is solidified to bond the reinforcing material tothe interior surface of the stator tube and then the mandrel is removedfrom the bonded stator tube and reinforcing material such that a statoris fabricated.

In accordance with one aspect of the present invention, the stator tubecomprises a material selected from the group consisting of: iron, steel,high speed steel, carbon steel, tungsten steel, brass, and copper.

Additionally, the bonding agent utilized in fabricating the stator maybe a single-layer bonding agent or a multiple-layer bonding agent.

In accordance with one aspect of the present invention, the mandrel maycomprise a material selected from the group consisting of: iron, steel,high speed steel, carbon steel, tungsten steel, brass, and copper.Additionally, the mandrel may be coated with a release agent havingnumerous forms including a solid, semi-solid or a liquid.

The reinforcing material of the present invention may take numerousforms as understood by one skilled in the art. For example, thereinforcing material may be a composite. In accordance with anotheraspect of the present invention, the reinforcing material may be apolymer. In accordance with a further aspect of the present invention,the reinforcing material may be a thermosetting plastic or athermoplastic.

As understood by one skilled in the art, the reinforcing material of oneaspect of the present invention may be selected from the groupconsisting of: epoxy resins, polyimides, polyketones,polyetheretherketones (PEEK), phenolic resins, and polyphenylenesulfides (PPS).

Additionally, the reinforcing material may be in various forms includinga liquid, a paste, a slurry, a power, and/or a granular form.Furthermore, the reinforcing material may be cross-linked and/or mayhave a high degree of crystallinity. In accordance with aspects of thepresent invention, when solidifying the reinforcing material to bond thereinforcing material to the interior surface of the stator tube varioustechniques may be utilized. These techniques may include, but are notlimited to the use of heat curing, radiation curing, steam curing, andcooling.

The present invention further claims a stator for a downhole motor, thestator comprising a stator tube including an inner surface and asolidified reinforcing material bonded to the inner surface, thesolidified reinforcing material having an inner surface defining aninternal helical cavity including a plurality of internal lobes.Additionally, the present invention recites a downhole motor comprisinga stator wherein said stator comprises a stator tube including an innersurface and a solidified reinforcing material bonded to the innersurface, the solidified reinforcing material having an inner surfacedefining an internal helical cavity including a plurality of internallobes and a rotor received within the stator. In accordance with thepresent invention, the rotor may be coated with an elastomer, whereinthe elastomer may comprise one or more selected from the groupconsisting of: rubber, natural rubber (NR), synthetic polyisoprene (IR),butyl rubber, halogenated butyl rubber, polybutadiene (BR), nitrilerubber, nitrile butadiene rubber (NBR), hydrogenated nitrile butadienerubber (HNBR), carboxylated hydrogenated nitrile butadiene rubber(XHNBR), chloroprene rubber (CR) Fluorocarbon rubber (FKM), andPerfluoroelastomers (FFKM).

DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and desired objects of thepresent invention, reference is made to the following detaileddescription taken in conjunction with the accompanying drawing figureswherein like reference characters denote corresponding parts throughoutthe several views and wherein:

FIG. 1 illustrates a wellsite system in which the present invention canbe employed;

FIGS. 2A-2C illustrate a Moineau-type positive displacement downholemotor having a 1:2 lobe profile according to one embodiment of theinvention;

FIGS. 3A-3F illustrate a Moineau-type positive displacement downholemotor having a 3:4 lobe profile according to one embodiment of theinvention;

FIGS. 4 and 5A-5D illustrate a method of producing a stator according toone embodiment of the invention;

FIGS. 6 and 7A-7D illustrate a method of producing a stator insertaccording to one embodiment of invention;

FIG. 8 illustrates a stator tube and a stator insert having a splinedgeometry according to one embodiment of the invention; and

FIG. 9 illustrates an alternative method of producing a stator accordingto one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention provide stators and stator inserts fordownhole motors, methods for fabricating the same, and downhole motorsincorporating the same. Various embodiments of the invention can be usedin wellsite systems.

Wellsite System

FIG. 1 illustrates a wellsite system in which the present invention canbe employed. The wellsite can be onshore or offshore. In this exemplarysystem, a borehole 11 is formed in subsurface formations by rotarydrilling in a manner that is well known. Embodiments of the inventioncan also use directional drilling, as will be described hereinafter.

A drill string 12 is suspended within the borehole 11 and has a bottomhole assembly (BHA) 100 which includes a drill bit 105 at its lower end.The surface system includes platform and derrick assembly 10 positionedover the borehole 11, the assembly 10 including a rotary table 16, kelly17, hook 18 and rotary swivel 19. The drill string 12 is rotated by therotary table 16, energized by means not shown, which engages the kelly17 at the upper end of the drill string. The drill string 12 issuspended from a hook 18, attached to a traveling block (also notshown), through the kelly 17 and a rotary swivel 19 which permitsrotation of the drill string relative to the hook. As is well known, atop drive system could alternatively be used.

In the example of this embodiment, the surface system further includesdrilling fluid or mud 26 stored in a pit 27 formed at the well site. Apump 29 delivers the drilling fluid 26 to the interior of the drillstring 12 via a port in the swivel 19, causing the drilling fluid toflow downwardly through the drill string 12 as indicated by thedirectional arrow 8. The drilling fluid exits the drill string 12 viaports in the drill bit 105, and then circulates upwardly through theannulus region between the outside of the drill string and the wall ofthe borehole, as indicated by the directional arrows 9. In thiswell-known manner, the drilling fluid lubricates the drill bit 105 andcarries formation cuttings up to the surface as it is returned to thepit 27 for recirculation.

The bottom hole assembly 100 of the illustrated embodiment includes alogging-while-drilling (LWD) module 120, a measuring-while-drilling(MWD) module 130, a roto-steerable system and motor, and drill bit 105.

The LWD module 120 is housed in a special type of drill collar, as isknown in the art, and can contain one or a plurality of known types oflogging tools. It will also be understood that more than one LWD and/orMWD module can be employed, e.g. as represented at 120A. (References,throughout, to a module at the position of 120 can alternatively mean amodule at the position of 120A as well.) The LWD module includescapabilities for measuring, processing, and storing information, as wellas for communicating with the surface equipment. In the presentembodiment, the LWD module includes a pressure measuring device.

The MWD module 130 is also housed in a special type of drill collar, asis known in the art, and can contain one or more devices for measuringcharacteristics of the drill string and drill bit. The MWD tool furtherincludes an apparatus (not shown) for generating electrical power to thedownhole system. This may typically include a mud turbine generator(also known as a “mud motor”) powered by the flow of the drilling fluid,it being understood that other power and/or battery systems may beemployed. In the present embodiment, the MWD module includes one or moreof the following types of measuring devices: a weight-on-bit measuringdevice, a torque measuring device, a vibration measuring device, a shockmeasuring device, a stick slip measuring device, a direction measuringdevice, and an inclination measuring device.

A particularly advantageous use of the system hereof is in conjunctionwith controlled steering or “directional drilling.” In this embodiment,a roto-steerable subsystem 150 (FIG. 1) is provided. Directionaldrilling is the intentional deviation of the wellbore from the path itwould naturally take. In other words, directional drilling is thesteering of the drill string so that it travels in a desired direction.

Directional drilling is, for example, advantageous in offshore drillingbecause it enables many wells to be drilled from a single platform.Directional drilling also enables horizontal drilling through areservoir. Horizontal drilling enables a longer length of the wellboreto traverse the reservoir, which increases the production rate from thewell.

A directional drilling system may also be used in vertical drillingoperation as well. Often the drill bit will veer off of a planneddrilling trajectory because of the unpredictable nature of theformations being penetrated or the varying forces that the drill bitexperiences. When such a deviation occurs, a directional drilling systemmay be used to put the drill bit back on course.

A known method of directional drilling includes the use of a rotarysteerable system (“RSS”). In an RSS, the drill string is rotated fromthe surface, and downhole devices cause the drill bit to drill in thedesired direction. Rotating the drill string greatly reduces theoccurrences of the drill string getting hung up or stuck duringdrilling. Rotary steerable drilling systems for drilling deviatedboreholes into the earth may be generally classified as either“point-the-bit” systems or “push-the-bit” systems.

In the point-the-bit system, the axis of rotation of the drill bit isdeviated from the local axis of the bottom hole assembly in the generaldirection of the new hole. The hole is propagated in accordance with thecustomary three-point geometry defined by upper and lower stabilizertouch points and the drill bit. The angle of deviation of the drill bitaxis coupled with a finite distance between the drill bit and lowerstabilizer results in the non-collinear condition required for a curveto be generated. There are many ways in which this may be achievedincluding a fixed bend at a point in the bottom hole assembly close tothe lower stabilizer or a flexure of the drill bit drive shaftdistributed between the upper and lower stabilizer. In its idealizedform, the drill bit is not required to cut sideways because the bit axisis continually rotated in the direction of the curved hole. Examples ofpoint-the-bit type rotary steerable systems and how they operate aredescribed in U.S. Pat. Nos. 6,394,193; 6,364,034; 6,244,361; 6,158,529;6,092,610; and 5,113,953; and U.S. Patent Application Publication Nos.2002/0011359 and 2001/0052428.

In the push-the-bit rotary steerable system there is usually nospecially identified mechanism to deviate the bit axis from the localbottom hole assembly axis; instead, the requisite non-collinearcondition is achieved by causing either or both of the upper or lowerstabilizers to apply an eccentric force or displacement in a directionthat is preferentially orientated with respect to the direction of holepropagation. Again, there are many ways in which this may be achieved,including non-rotating (with respect to the hole) eccentric stabilizers(displacement based approaches) and eccentric actuators that apply forceto the drill bit in the desired steering direction. Again, steering isachieved by creating non co-linearity between the drill bit and at leasttwo other touch points. In its idealized form, the drill bit is requiredto cut side ways in order to generate a curved hole. Examples ofpush-the-bit type rotary steerable systems and how they operate aredescribed in U.S. Pat. Nos. 6,089,332; 5,971,085; 5,803,185; 5,778,992;5,706,905; 5,695,015; 5,685,379; 5,673,763; 5,603,385; 5,582,259;5,553,679; 5,553,678; 5,520,255; and 5,265,682.

Downhole Motors

Referring now to FIGS. 2A-2C, a Moineau-type positive displacementdownhole motor 200 is depicted. Downhole motor 200 includes a rotor 202received within a stator 204. Rotor 202 can be a helical memberfabricated from a rigid material such metals, resins, composites, andthe like. Stator 204 can have an oblong, helical shape and be fabricatedfrom elastomers that allow for the rotor 202 to rotate within the stator204 as fluid flows between chambers 206 formed between the rotor 202 andthe stator 204. In some embodiments, stator 204 is received withinstator tube 208 that can partially limit the deformation of the stator204 as the rotor 202 rotates and can protect the exterior of stator 204from wear.

Downhole motors 200 can be fabricated in a variety of configurations.Generally, when viewed as a latitudinal cross-section as depicted inFIG. 1B, rotor 202 has n_(r) lobes and stator 204 has n_(s) lobes,wherein n_(s)=n_(r)+1. For example, FIGS. 2A-2C depict a downhole motor200 with a 1:2 lobe profile, wherein rotor 202 has one lobe 210 andstator 204 has two lobes 212. FIGS. 3A-3F depict a downhole motor 300with a 3:4 lobe profile, wherein rotor 302 has three lobes 310 andstator 304 has four lobes 312. Other exemplary lobe profiles include5:6, 7:8, 9:10, and the like.

The rotation of rotor 302 is depicted in FIGS. 3C-3F.

Downhole motors are further described in a number of publications suchas U.S. Pat. Nos. 7,442,019; 7,396,220; 7,192,260; 7,093,401; 6,827,160;6,543,554; 6,543,132; 6,527,512; 6,173,794; 5,911,284; 5,221,197;5,135,059; 4,909,337; 4,646,856; and 2,464,011; U.S. Patent ApplicationPublication Nos. 2009/0095528; 2008/0190669; and 2002/0122722; andWilliam C. Lyons et al., Air & Gas Drilling Manual: Applications for Oil& Gas Recovery Wells & Geothermal Fluids Recovery Wells §11.2 (3d ed.2009); G. Robello Samuel, Downhole Drilling Tools: Theory & Practice forEngineers & Students 288-333 (2007); Standard Handbook of Petroleum &Natural Gas Engineering 4-276-4-299 (William C. Lyons & Gary J. Plisgaeds. 2006); and 1 Yakov A. Gelfgat et al., Advanced Drilling Solutions:Lessons from the FSU 154-72 (2003).

Methods of Producing Stators

Referring now to FIG. 4 in the context of FIGS. 5A-5D, a method 400 ofproducing a stator 500 is provided. Lateral slices without depth aredepicted in FIGS. 5A-5D for ease of illustration and comprehension.

In step S402, a stator tube 502 is provided. As discussed herein, statortube 502 can be a rigid material. For example, stator tube 502 can befabricated from iron, steel, high speed steel, carbon steel, tungstensteel, brass, copper, and the like.

Optionally, in step S404, the interior surface of the stator tube 502 isprepared. In some embodiments, a worn stator insert is removed from thestator tube 502. In other embodiments, the inner surface of the statortube 502 is cleaned, degreased, sand blasted, shot blasted, and thelike.

In step S406, a bonding agent 504 is applied to the interior surface ofthe stator tube 502. The bonding agent 504 can be a single-layer bondingagent or a multiple-layer bonding agent. One skilled in the art willrecognize that numerous suitable bonding agents existing, including butnot limited to epoxy resin, phenolic resin, polyester resin or anynumber of suitable alternatives.

In step S408, a mandrel 506 is positioned within the stator tube 502.Preferably the mandrel 506 is centered within the stator tube 502 suchthat the longitudinal axis of the mandrel 506 is coaxial with thelongitudinal axis of the stator tube 502. The mandrel 506 has an outergeometry that is complimentary to a desired inner geometry of the stator500 to be produced. For example, mandrel 506 can have an oblong, helicalshape and have ns lobes (e.g., four lobes in the embodiment depicted inFIG. 5A).

In some embodiments, the mandrel 506 is coated with a release agent (notdepicted) to promote removal of the mandrel 506. Additionally oralternatively, one or more resilient layers 508 can be applied to themandrel 506 (e.g., over the release agent) to strengthen the stator 500.For the purpose of clarity, the term reinforcing/resilient layer will beused interchangeably within the present specification. For example, aresilient layer 508 can be formed from an elastomers such as rubber,natural rubber (NR), synthetic polyisoprene (IR), butyl rubber,halogenated butyl rubber, polybutadiene (BR), nitrile rubber, nitrilebutadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR),carboxylated hydrogenated nitrile butadiene rubber (XHNBR), chloroprenerubber (CR), and the like. In still another embodiment, the resilientlayer 508 can be reinforced with a fiber or textile such as poly-aramidsynthetic fibers such as KEVLAR® fiber available from E.I. Du Pont deNemours and Company of Wilmington, Del.

In some embodiments, a bonding agent (not depicted) is applied to theresilient layer 508. The bonding agent can be a single-layer bondingagent or a multiple-layer bonding agent.

In step S410, a reinforcing material 510 is introduced into the statortube 502. Examples of suitable reinforcing materials 510 are discussedherein.

In step S412, the reinforcing material 510 is solidified as discussedherein.

In step S414, the mandrel 506 is removed from the solidified stator 500.

Methods of Producing Stator Inserts

Referring now to FIG. 6 in the context of FIGS. 7A-7D, a method 600 ofproducing stator inserts is provided. Lateral slices without depth aredepicted in FIGS. 7A-7D for ease of illustration and comprehension.

In step S602, a mandrel 702 is provided. The mandrel 702 has an outergeometry that is complimentary to a desired inner geometry of the statorinsert to be produced. For example, mandrel 702 can have an oblong,helical shape and have n_(s) lobes (e.g., four lobes in the embodimentdepicted in FIG. 7A).

In step S604, a flexible sleeve 704 is applied over mandrel 702. Theflexible sleeve 704 can be an elastomer. For example, the elastomers canbe rubber, natural rubber (NR), synthetic polyisoprene (IR), butylrubber, halogenated butyl rubber, polybutadiene (BR), nitrile rubber,nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber(HNBR), carboxylated hydrogenated nitrile butadiene rubber (XHNBR),chloroprene rubber (CR), Fluorocarbon rubber (FKM), Perfluoroelastomers(FFKM) and the like. In still another embodiment, the flexible sleeve704 can be reinforced using a fiber or textile such as poly-aramidsynthetic fibers such as KEVLAR® fiber available from E.I. Du Pont deNemours and Company of Wilmington, Del.

In some embodiments, a lubricant or release agent (e.g., liquids, gels,and/or powders) are applied between the flexible sleeve 704 and mandrel702 to facilitate insertion and removal of the mandrel 702. Preferably,the lubricant/release layer is compatible with the mandrel 702 and theflexible sleeve 704. One skilled in the art will recognize that thislubricant/release layer may take numerous forms, including but notlimited to a permanent or semi-permanent layer having a solid or liquidform.

Optionally, in step S606, a vacuum is applied between the flexiblesleeve and the mandrel to cause the flexible sleeve 704 to betterconform to the geometry of the mandrel 702. In some embodiments, avacuum is not needed as the flexible material 704 conforms to themandrel geometry without the need for physical manipulation.

In step S608, the assembled flexible sleeve 704 and mandrel 702 areplaced within a mold 706. Preferably the mandrel 702 is centered withinthe mold 706 such that the longitudinal axis of the mandrel 702 iscoaxial with the longitudinal axis of the mold 706. In some embodiments,inner geometry of the mold 706 is complimentary to the stator tube 708into which the molded stator insert will be installed (less anyallowances for adhesives 710, expansion, contraction, and the like). Forexample, the stator insert can have a substantially circular outerprofile and the stator tube 708 can have a substantially circular innerprofile.

In another embodiment depicted in FIG. 8, the stator tube 808 can have aplurality of splines 812 and stator insert 814 can include a pluralityof complimentary splines to provide mechanical retention of the statorinsert 814 within the stator tube 808. In accordance with an alternativeembodiment, one skilled in the art will readily recognize that theinside and outside walls of the stator tube are not necessarilyparallel.

In step S610, a reinforcing material 714 is introduced into the mold.Examples of suitable reinforcing materials 714 are discussed herein.

Optionally, a release agent and/or a lubricant can be applied to theinterior surface of mold 706 prior to the introduction of thereinforcing material 714 in order to promote removal of the solidifiedstator insert from the mold 706.

Additionally or alternatively, a bonding agent (not depicted) can beapplied to the flexible sleeve 704 prior to the introduction of thereinforcing material 714 in order to promote bonding of the reinforcingmaterial 714 with the flexible sleeve 704.

In step S612, the reinforcing material 714 is solidified as discussedherein.

In step S614, the solidified reinforcing material 714 and the flexiblesleeve 704 are removed from the mold 706. In some embodiments, theexterior surface of the solidified stator insert is treated to promotebetter bonding with stator tube 708. For example, the solidified statorinsert can be cleaned, degreased, sand blasted, shot blasted, and thelike.

In step S616, the mandrel 702 is optionally removed from the solidifiedstator insert prior to insertion of the stator into the stator tube 708in step S618. In another embodiment, mandrel 702 is removed from thesolidified stator insert after insertion into the stator tube 708.

A variety of techniques can be used to prepare the stator tube 708 toreceive the solidified stator insert. In some embodiments, a worn statorinsert is removed from the stator tube 708. In other embodiments, theinner surface of the stator tube 708 is cleaned, degreased, sandblasted, shot blasted, and the like.

In some embodiments, the stator insert is coupled to the inner surfaceof the stator tube 708. The stator insert can be coupled to the statortube 708 with an adhesive 710. For example, the adhesive 710 can beapplied to the outside of the stator insert and/or the inside of thestator tube 708. Alternatively, the adhesive 710 can be flowed orinjected, at pressure or under vacuum, between the stator insert and thestator tube 708 after the stator insert is inserted. A variety ofadhesives 710 can be used including epoxies, poly(methylmethylacrylate), polyurethane-based adhesives, and the like.

Reinforcing Materials and Methods of Solidifying

The reinforcing materials 510, 714 discussed herein can be a variety ofmaterials including composites, polymers, thermosetting plastic,thermoplastics, and the like. Exemplary polymers include epoxy resins,polyimides, polyketones, polyetheretherketones (PEEK), phenolic resins,polyphenylene sulfides (PPS), and the like. The reinforcing materials510, 714 can be introduced in a variety of forms including a liquid, apaste, a slurry, a powder, a granular form, and the like. In accordancewith aspects of the present invention, the reinforcing materials mayinclude, but are not limited to numerous liquids, pastes or powders thatmay be solidified. In accordance with one aspect of the presentinvention, these may be ceramics or cements.

The reinforcing materials 510, 714 can be cross-linked. Additionally oralternatively, the reinforcing materials 510, 714 can have a high degreeof crystallinity.

Solidifying of reinforcing materials 510, 714 may be accomplished by avariety of techniques including chemical additives, ultravioletradiation, electron beams, heating, exposure to either a part or thefull microwave spectrum, steam curing, cooling, and the like.Solidifying processes may vary between particular reinforcing materials510, 714, but can be ascertained from manufacturer's specifications andgeneral chemistry principles. In some embodiments, the reinforcingmaterial 510, 714 is solidified under pressure to promote bonding and/orincrease mechanical properties with the resilient layers 508 or flexiblesleeve 704, to press the resilient layers 508 or flexible sleeve 704against the geometry of mandrel 506, 702, and to improve the mechanicalproperties of the reinforcing materials 510, 174. For example,experiments reveal improvements of about 20% in T_(g), stiffness, andtoughness when the reinforcing material is solidified under pressure.

Additional Methods of Producing Stators

Referring now to FIG. 9 in the context of FIGS. 5A-5D, a method 900 ofproducing a stator 500 is provided. Lateral slices without depth aredepicted in FIGS. 5A-5D for ease of illustration and comprehension.

In step S902, a mandrel 506 is provided. The mandrel 506 can have anouter geometry that is complimentary to the desired inner geometry forthe stator 500. For example, mandrel 506 can have an oblong, helicalshape and have ns lobes (e.g., four lobes in the embodiment depicted inFIG. 5A).

Optionally, in step S904, the mandrel 506 can be coated with a releaseagent (not depicted) to promote removal of the mandrel 506 from theflexible sleeve 508.

In step S906, a flexible sleeve 508 is applied over the mandrel 506. Theflexible sleeve 508 can be formed from an elastomers such as rubber,natural rubber (NR), synthetic polyisoprene (IR), butyl rubber,halogenated butyl rubber, polybutadiene (BR), nitrile rubber, nitrilebutadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR),carboxylated hydrogenated nitrile butadiene rubber (XHNBR), chloroprenerubber (CR), Fluorocarbon rubber (FKM), Perfluoroelastomers (FFKM) andthe like. In still another embodiment, the flexible sleeve 508 can bereinforced with a fiber or textile such as poly-aramid synthetic fiberssuch as KEVLAR® fiber available from E.I. Du Pont de Nemours and Companyof Wilmington, Del.

Optionally, in step S908, a bonding agent (not depicted) is applied tothe exterior surface of the flexible sleeve 508. The bonding agent canbe a single-layer bonding agent or a multiple-layer bonding agent.

In step S910, a stator tube 502 is provided. As discussed herein, statortube 502 can be a rigid material. For example, stator tube 502 can befabricated from iron, steel, high speed steel, carbon steel, tungstensteel, brass, copper, and the like.

Optionally, in step S912, the interior surface of the stator tube 502 isprepared. In some embodiments, a worn stator insert is removed from thestator tube 502. In other embodiments, the inner surface of the statortube 502 is cleaned, degreased, sand blasted, shot blasted, and thelike.

In step S914, a bonding agent 504 is applied to the interior surface ofthe stator tube 502. The bonding agent 504 can be a single-layer bondingagent or a multiple-layer bonding agent. In accordance with the presentinvention a variety of Bonding agents may be use, including but notlimited to Hunstman CW47/HY33 or Chemosil 310. In step S916, theflexible sleeve 508 and mandrel 506 is positioned within the stator tube502. Preferably the mandrel 506 and flexible sleeve 508 is centeredwithin the stator tube 502 such that the longitudinal axis of themandrel 506 is coaxial with the longitudinal axis of the stator tube502.

In step S918, a reinforcing material 510 is introduced to fill the spacebetween flexible sleeve 508 and the stator tube 502. Examples ofsuitable reinforcing materials 510 are discussed herein.

In step S920, the reinforcing material 510 is solidified as discussedherein.

Optionally, in step S922, the mandrel 506 is removed from the stator500.

INCORPORATION BY REFERENCE

All patents, published patent applications, and other referencesdisclosed herein are hereby expressly incorporated by reference in theirentireties by reference.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents of the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

1. A method of fabricating a stator for a downhole motor, the methodcomprising: providing a stator tube having an interior surface; applyinga bonding agent to the interior surface of the stator tube; positioninga mandrel within the stator tube, the mandrel having an outer geometrythat is complimentary to a desired inner geometry for the stator;introducing a reinforcing material into the stator tube to fill spacebetween the mandrel and the interior surface of the stator tube;solidifying the reinforcing material to bond the reinforcing material tothe interior surface of the stator tube; and removing the mandrel fromthe bonded stator tube and reinforcing material; thereby fabricating thestator.
 2. The method of claim 1, wherein the stator tube comprises amaterial selected from the group consisting of: iron, steel, high speedsteel, carbon steel, tungsten steel, brass, and copper.
 3. The method ofclaim 1, wherein the bonding agent is a single-layer bonding agent. 4.The method of claim 1, wherein the bonding agent is a multiple-layerbonding agent.
 5. The method of claim 1, wherein the mandrel comprises amaterial selected from the group consisting of: iron, steel, high speedsteel, carbon steel, tungsten steel, brass, and copper.
 6. The method ofclaim 1, wherein the mandrel is coated with a release agent.
 7. Themethod of claim 1, wherein the reinforcing material is a composite. 8.The method of claim 1, wherein the reinforcing material is a polymer. 9.The method of claim 8, wherein the reinforcing material is athermosetting plastic.
 10. The method of claim 8, wherein thereinforcing material is a thermoplastic.
 11. The method of claim 8,wherein the reinforcing material comprises one or more selected from thegroup consisting of: epoxy resins, polyimides, polyketones,polyetheretherketones (PEEK), phenolic resins, and polyphenylenesulfides (PPS).
 12. The method of claim 1, wherein the reinforcingmaterial is in a form selected from the group consisting of: a liquid, apaste, a slurry, a power, and granular.
 13. The method of claim 1,wherein the reinforcing material is cross-linked.
 14. The method ofclaim 1, wherein the reinforcing material has a high degree ofcrystallinity.
 15. The method of claim 1, wherein the step ofsolidifying the reinforcing material to bond the reinforcing material tothe interior surface of the stator tube further comprises one ortechniques selected from the group consisting of: heat curing, radiationcuring, steam curing, and cooling.
 16. A stator for a downhole motor,the stator comprising: a stator tube including an inner surface; and asolidified reinforcing material bonded to the inner surface, thesolidified reinforcing material having an inner surface defining aninternal helical cavity including a plurality of internal lobes.
 17. Adownhole motor comprising: a stator comprising: a stator tube includingan inner surface; and a solidified reinforcing material bonded to theinner surface, the solidified reinforcing material having an innersurface defining an internal helical cavity including a plurality ofinternal lobes; and a rotor received within the stator.
 18. The downholemotor of claim 17, wherein the rotor is coated with an elastomer. 19.The downhole motor of claim 18, wherein the elastomer comprises one ormore selected from the group consisting of: rubber, natural rubber (NR),synthetic polyisoprene (IR), butyl rubber, halogenated butyl rubber,polybutadiene (BR), nitrile rubber, nitrile butadiene rubber (NBR),hydrogenated nitrile butadiene rubber (HNBR), carboxylated hydrogenatednitrile butadiene rubber (XHNBR), chloroprene rubber (CR) Fluorocarbonrubber (FKM), and Perfluoroelastomers (FFKM).